This invention relates to prosthetic devices for replacement, reconstruction and attachment in the skeletal system of humans and animals, and, more particularly, to a process for fabricating a titanium alloy mesh bone in-growth surface for use in such devices.
Prosthetic devices are used to partially or completely replace joints or bone segments in the skeletal structure of humans or animals. One of the major problems involved in the use of prosthetic devices is the attachment of the prosthetic implant to the adjacent bone. There are four principle methods of which the device can be attached to the bone: (1) force fitting the implant into the medullary canal of the bone; (2) securing the implant in the bone with the aid of screws or pins; (3) bonding the implant by a plastic methyl methacrylic resin which is polymerized "in situ"; and (4) employing in conjunction with the implant a porous material into which the bone may grow.
Each of the first three approaches suffers from one or more advantages, as is well-known. More recently, several variations of the fourth approach have been employed. Examples of these are found in U.S. Pat. Nos. 3,905,777, 3,852,045, 3,886,600, 4,089,071, 4,439,152, 3,906,550 and 4,261,063. While some of these patents do not disclose how the porous material, or mesh, is formed, the patents that do make such disclosure typically teach a sintering process, employing temperatures on the order of 1000.degree. to 1350.degree. C. (1958.degree. to 2462.degree. F.) for titanium and titanium alloys. As is well-known, titanium and titanium alloys (particularly Ti-6Al-4V) are often used in prosthetic devices, due to their biocompatibility. The sintering temperatures employing in fabricating meshes made from such materials results in a degradation of the physical properties of the material. In particular, fatigue values are reduced by more than 50% by the sintering process.
Further, the processes described in the foregoing patents [e.g., U.S. Pat. No. 3,905,777 (layers of perforated foil welded together), U.S. Pat. No. 3,852,045 (sintered particles), or U.S. Pat. No. 3,906,550 (short metal fibers compacted and sintered)] result in meshes that may be considered to be poorly characterized in that the physical properties of strength are not uniform over the surface of the mesh. The non-uniformity of strength, of course, reduces the usefulness of the mesh. Also, such meshes evidence a poorly characterized mesh density, in that the mesh density is variable, with consequent varying degree of bone ingrowth and penetration. The non-uniform bone penetration also reduces the usefulness of the mesh.
Many of the known bone in-growth surface coatings do not readily permit fabrication of custom prostheses. Rather, custom prostheses, if at all possible, are either expensive or take a long time to make by virtue of the necessity of creating special fixturing and jigging.